1. Field of the Invention
This invention relates to a technology for controlling a memory in a dual memory system.
2. Description of the Related Art
A technology is conventionally disclosed that enhances reliability in a data processing device and the like by employing a redundant memory system that uses, for example, a DIMM (Dual Inline Memory Module) in a data processing device.
For example, in Japanese Patent Application Laid-Open No. H7-160587, a technology is disclosed that enhances reliability in a redundant memory system by managing trouble information in an address unit at the time of an initial diagnosis of a redundant memory system and, even when a fixing trouble of equal to or more than 2 bits is detected at one line of redundant memory, performing changing to the other line to efficiently utilize a capability of recovering. More specifically, when a fixing trouble of equal to or more than 2 bits is detected at one half of redundant memory at the time of an initial diagnosis, reliability of a redundant memory system is improved by indicating only an address of the corresponding memory as invalid or valid, outputting an invalid signal concerning the address to disable a comparison circuit, and indicating that an address is valid and use of data in memory that has an address in which a parity error is not detected.
However, the above conventional technology has a problem that trouble information cannot be handled in real time and a system down may occur.
That is, the above conventional technology is a technology to enhance reliability in a redundant memory system based on trouble information in initial diagnosis of a redundant memory system. Thus, the technology has a problem that it is impossible to deal with trouble information that is informed in activating a system.
An error on an address line of a DIMM that is a redundant memory system is not supported in the above conventional technology. Therefore, when an error occurs on an address line, it cannot be recognized and then it is even hazardous to use data of a wrong address. In a technology of constituting one ECC (Error Correcting Code) error check unit through a plurality of DIMMs (for example, two DIMMs) to avoid the hazard, there is a possibility that coincidence of ECCs that occurs at a certain probability causes error data. Occurrence of error data through accidental coincidence of ECCs, when a line of redundant memory is changed to recover an error, makes it difficult to determine which line to select, thereby causing a problem that a system down may occur.